1. Technical Field
The present invention relates to a ZnO film, and more particularly, to a ZnO film structure using a growth mask, and a method of forming the same.
2. Description of the Related Art
ZnO has an optical bandgap of 3.37 eV, which is similar to gallium nitride, and may be used as a light source of a near ultraviolet region. In addition, in the case in which ZnO is used to manufacture an optical device, it may secure good quality due to high defect formation energy. In addition, exciton binding energy at room temperature is 60 mev, which is three times higher than that (24 meV) of gallium nitride. Therefore, in a field using an optical device using exciton, a high efficiency optical gain effect may be obtained.
However, at the time of manufacturing a light emitting diode based on ZnO, there is a problem that an optical output is low. This is due to high dislocation density formed in a ZnO film in a process of actually forming the ZnO film as compared with a theoretical advantage. In the case of a ZnO based light emitting diode, dislocation density formed in a film is 1011 cm−2, which is higher than dislocation density (108 cm−2) of a gallium nitride based light emitting diode that has been commercialized. The ZnO based light emitting diode has optical efficiency lower than that of the gallium nitride based light emitting diode due to the high dislocation density. Therefore, in the case of decreasing the dislocation density of the ZnO based light emitting diode, very high optical efficiency may be secured.
In the gallium nitride based light emitting diode, an SiO2 mask is used in order to decrease the dislocation density formed in a film. The SiO2 mask is used, such that an epitaxial lateral overgrowth (ELOG) technology is used in a selective region. Therefore, dislocation transferred from a substrate is blocked by the SiO2 mask, and dislocation density in the gallium nitride film is decreased. To this end, direct growth of the film on the SiO2 mask should be suppressed and lateral growth should be induced so that the gallium nitride film grown from an opened region under the SiO2 mask cover an upper surface of the SiO2 mask.
The SiO2 mask has an advantage that the ELOG technology may be easily used. On the other hand, in the case of growing the ZnO film using the SiO2 mask, a problem that the ZnO film is directly formed on the SiO2 mask occurs. Therefore, it is difficult to form a ZnO single crystal and it is impossible to apply the ELOG technology.
Accordingly, in order to grow a ZnO film, it is requisite to develop a new mask capable of growing the ZnO film in a selective region.